Device for determining the crystallographic directions in single crystals by x-rays

ABSTRACT

A device for determining the crystallographic directions in single crystals comprises a holder for a single crystal, a source of primary X-rays, e.g., an X-ray tube, and a recording surface for receiving and recording X-rays reflected by the lattice planes of the crystal, e.g., diffracted X-rays. In order to increase the accuracy of the measurement, the crystal is ground to provide a reference surface the normal of which is inclined at a small angle relative to the path of the beam of primary X-rays which are incident thereon. The film for receiving and registering the reflected X-rays from the lattice planes of the crystal is located to one side of the path of the primary X-ray beam and is so positioned that the normal to the surface of the film is rotated relative to the primary X-ray beam by twice the angle between the normal to the smooth surface of the crystal and the central ray of the primary X-ray beam. Preferably, the crystal is mounted in a holder which with the film are arranged on a common base plate.

Unite States Patent Eckerlin [54] DEVICE FOR DETERMINING THECRYSTALLOGRAPHIC DIRECTIONS IN SINGLE CRYSTALS BY X-RAYS [72] Inventor:Peter Eckerlin, Aachen, Germany [73] Assignee: U. S. PhilipsCorporation, New York, N.Y.

[22] Filed: June 23, 1969 [21 Appl. No.: 835,611

[ Mar. 14, 1972 Primary ExaminerJames W. Lawrence Assistant Examiner-A.L. Birch Attorney-Frank R. Trifari [5 7] ABSTRACT A device fordetermining the crystallographic directions in single crystals comprisesa holder for a single crystal, a source of primary X-rays, e.g., anX-ray tube, and a recording surface for receiving and recording X-raysreflected by the lattice planes of the crystal, e. g., diffractedX-rays. In order to increase the accuracy of the measurement, thecrystal is ground to provide a reference surface the normal of which isinclined at a small angle relative to the path of the beam of primary X-rays which are incident thereon. The film for receiving and registeringthe reflected X-rays from the lattice planes of the crystal is locatedto one side of the path of the primary X-ray beam and is so positionedthat the normal to the surface of the film is rotated relative to theprimary X-ray beam by twice the angle between the normal to the smoothsurface of the crystal and the central ray of the primary X-ray beam.

Preferably, the crystal is mounted in a holder which with the film arearranged on a common base plate.

4Claims, 2 Drawing Figures DEVICE FOR DETERMINING THE CRYSTALLOGRAPHICDIRECTIONS IN SINGLE CRYSTALS BY X-RAYS The invention relates to adevice for determining the crystallographic directions in singlecrystals relative to an available flat surface by means of X-rays. Thissurface is provided by mechanical processing approximately parallel to apredetermined lattice plane of low index and will be termed hereinafterthe reference surface. Its position can be adjusted by simple means forcoarse setting with an accuracy of about 1 parallel to the preferentialplane. This accuracy is usually not sufficient and there has beenproposed a Laue reflection method which permits in routine operationdetermining considerably smaller discrepancies. Reflections produced byincident X-rays are registered on a photographic plate.

The purpose is to find the accurate positions of the two normals that ofthe lattice plane and that of the reference plane relative to eachother. Two graphs are made on the same film, the crystal being turned inthe first graph through 180 about the normal to the reference plane sothat in the case where the reference plane and the lattice plane are notparallel the latter will swing and identical reflections on the graphare separated. The position of the reflections is determined by theangle of swinging and the position relative to the crystal or bycorresponding components of the angle of swinging relative to definitecrystal marks.

Basically the Laue reflection method is involved here in which the filmis arranged at right angles to the central ray of the X-ray beam, theX-ray penetrating through an opening of the film, while the crystal isadjusted by its reference surface to the X-rays. This surface is not atright angles to the X-ray beam, but it is slightly inclined so that thenormal to the surface at the spot of incidence of the X-rays deviatesfrom the normal and is directed approximately to a spot midway betweenthe edge and the opening for the primary ray in the photographic film.Therefore, even with a slight deviation of the desired lattice planerelative to the reference surface the reflections ofthe lattice planecannot fall into the primary ray opening.

In this method of measurement the localisation of the target point ofthe normal to the surface on the film is dispensed with, because thispoint can never be reproduced with full accuracy. By turning the crystalthrough 180 about its normal to the surface and by a subsequent furtherexposure of the film, reflections of the desired lattice plane areobtained, which are separated by four times the angle of rotation andare located substantially symmetrically with respect to the point ofimpact ofthe surface normal in the target plane ofthe X-rays.

The accuracy of the measurement is related particularly to the correctdetermination of the distance of the reflections on the film and thedistance between film and crystal, and from measured results obtainedthe deviation of the normal to the lattice plane from the normal to thereference surface can be calculated. An arrangement which isparticularly advantageous is that in which the position of the referencesurface of the crystal relative to the photographic film can beaccurately determined. The known arrangement involves the difficultythat the normal to the reference surface is obliquely incident to thefilm so that a deformation of the diffraction image disturbing themeasurement has to be taken into ac count, Moreover, the thus farunavoidable scattering of the primary rays on the film has a slightlydisturbing background effect in the range of the reflection positionsdeviating comparatively slightly from the central ray of the X-ray beam.

The invention has for its object to avoid these disadvantages in adevice of the kind set forth having a target crystal surface to beexamined inclined to the primary X-rays. According to the invention theregistering surface i.e., the film for the X- rays reflected by thelattice planes of the crystal to be examined is located adjacent thepath of the primary rays, while this registering surface occupies aposition in which the normal to the surface is rotated relative to theprimary X-ray beam by twice the angle between the normal to the smoothsurface of the crystal and the central ray of the primary X-ray beam.Preferably the film and crystal holders are arranged on a common baseplate so that the distance of the film from the reference plane can beadjusted and definitely mixed. The distance between film and referenceplane can then be accurately determined by means of a single calibratinggraph with the aid of a cubic single crystal by using reflections fromsymmetrical lattice planes whose angle is accurately known as a resultof the cubic symmetry.

The drawing shows details of the device according to the invention, inwhich FIG. 1 is an elevation and FIG. 2 is a side elevation.

A base plate 1, which is slidable along a support 2, is provided with acrystal holder 3 and a holder 4 for the collimator 5 of the X-ray beamto be used for the examination. The X-ray beam emanates from an X-raytube (not shown), arranged in a supporting column 6 and passes throughan exit opening 7 in the wall 8 of the column 6 into the collimator 5.The entrance opening 9 of the collimator 5 has a size of l to 1.5 mm.and the end is constructed so that all stray rays are withheld. The exitopening 10 has a size of about 0.3 mm.

The crystal holder 3 is arranged on a support 11 on the base plate 1 andhas a flat surface 12 of ground stainless noble steel. The slide 13remote from the X-ray incidence is the counterface for the referencesurface by which a crystal is urged against the surface 13 by means of ascrew 14 via a head 15 resiliently held therein. The plate 12 has aconical opening 16, through which the X-rays can strike the crystal andthe reflections can emanate.

By means of a screw 17 the base plate 1 can be fixed to the support 2,which is fastened by an angle-section arm 18 to the column 6. The latteris held by a base 19.

The rays reflected from the crystal are captured by a film 21 in a filmcassette 20, which may be a conventional flat cassette. It is fastenedto a rear wall 22, which is held by an arm 23 on the base plate.

In order to determine by this device the deviations of the normal toground, smooth surfaces of single crystals from the normal to thelattice plane, the crystal is clamped in a position well defined withrespect to its external shape. The flat ground surface 13 of the crystalholder plate 12 is turned relatively to the main direction of the beam,that is to say the normal to the surface 24 is inclined to the X-raybeam by an angle a, which allows the film 21 to be disposed at the sideof the X-ray collimator 5 for capturing the resultant reflections. Inorder to ensure a minimum deformation of the diffraction image, the film21 is turned through an angle 201 between the normal 25 to the film andthe X-ray.

This disposition guarantees a great accuracy of the measurements, whichin a measuring range from 4' to 6 without optical expedients is about 2and in a measuring range from 2 to 3 can be reduced to about 1'.

The distance between the film and the reference surface is adjustableover a restricted length by means of the screws 26 and 27, between whichthe support 11 of the crystal holder 3 is clamped so that this distancecan be accurately adjusted and fixed definitely.

What is claimed is:

1. In a device for determining the crystallographic directions in singlecrystals by a primary beam of X-rays relative to a smooth surface on thecrystal, in which X-rays reflected from the crystal are registered on aphotographic plate, and the smooth surface of the crystal is inclined tothe central ray of the primary X-ray beam, the improvement wherein therecording surface for the X-rays reflected by the crystal is locatedadjacent the path of the primary rays in a position in which a normal tothe recording surface is turned through twice the angle between thenormal to the smooth surface of the crystal and the central ray of theprimary X-ray beam.

2. A device as claimed in claim 1, wherein a holder for the recordingsurface and a holder for the crystal are arranged on a common baseplate.

reflected by given lattice planes of the crystal, said detector beingpositioned adjacent the path of the primary X-ray beam and having agiven receiving surface on which the reflected X- rays are incident,said detector receiving surface having a normal which forms an anglewith the central ray of said primary X-ray beam which is twice thatformed between the normal to the crystal reference surface and theprimary X-ray beam.

* k II i

1. In a device for determining the crystallographic directions in singlecrystals by a primary beam of X-rays relative to a smooth surface on thecrystal, in which X-rays reflected from the crystal are registered on aphotographic plate, and the smooth surface of the crystal is inclined tothe central ray of the primary X-ray beam, the improvement wherein therecording surface for the X-rays reflected by the crystal is locatedadjacent the path of the primary rays in a position in which a normal tothe recording surface is turned through twice the angle between thenormal to the smooth surface of the crystal and the central ray of theprimary X-ray beam.
 2. A device as claimed in claim 1, wherein a holderfor the recording surface and a holder for the crystal are arranged on acommon base plate.
 3. A device as claimed in claim 2, wherein the holderfor the crystal is adjustable in the direction of the X-rays.
 4. Adevice for determining the crystallographic directions in a singlecrystal comprising means to generate a beam of primary X-rays, means toposition the single crystal with a given reference surface the normal towhich forms a given angle with the central ray of the primary X-ray beamincident thereon, a detector for receiving and recording X-raysreflected by given lattice planes of the crystal, said detector beingpositioned adjacent the path of the primary X-ray beam and having agiven receiving surface on which the reflected X-rays are incident, saiddetector receiving surface having a normal which forms an angle with thecentral ray of said primary X-ray beam which is twice that formedbetween the normal to the crystal reference surface and the primaryX-ray beam.